Bearing materials

ABSTRACT

The invention is a bearing material of which a major constituent is aluminum characterised by between 1 percent and 16 percent (preferably between 3 percent and 7 percent or between 7 percent and 10 percent or between 10 percent and 16 percent of bismuth by weight, and optionally including 0 - 3 percent copper, 0 - 3 percent nickel, 0 - 3 percent manganese, 0 - 11 percent silicon.

United States Patent, 1 1 [111 3,753,695

Lloyd Aug. 21, 1973 [54] BEARING MATERIALS 2,752,240 6/1956 Schluchter75/148 2,026,546 1/1936 Kem fet al.. 75/138 [751 Invent! Kenneth Loud,Eula 3,410,331 11/1968 Mille et al. 75/138 [73] Assignee: The GlacierMetal Company Limited, Alperton, England Primary Examiner-Richard 0.Dean Flled: 111 1971 Attorney-Pierce, Schefiler & Parker 211 Appl. No.:114,660

[30] Foreign Application Priority Data [57] ABSTRACT Feb. 13, 1970 GreatBritain 7,058/70 The invention is a bearing material of which a major Cl38, constituent is aluminum characterised by between 1 75/139, 75/144,75/148 percent and 16 percent (preferably between 3 percent [51] Int.Cl. C22c 21/02 and 7 percent or between 7 percent and 10 percent or [58]Field of Search 75/138, 139, 143, between 10 percent'and 16 percent ofbismuth by 1 75/148, 144; 148/32, 32.5; 29/ 196.2 weight, and optionallyincluding 0 3 percent copper, 1 i 0 3 percent nickel, O 3 percentmanganese, 0 1 l [56] References Cited percent silicon.

UNITED STATES PATENTS 3,562,884 2/1971 Webbere 75/138 5 Claims, 1Drawing Figure o TEST CONDITIONS= 450 RPM. N f l6lb.APPLlED LOAD 0 Al l/0 Cu l/o N1+Sn No LUBRCATON El Al- 1% Cu+Sn 11 t 01 j 400 u u 4, O 2 46 8 1o 12 14 1e 1s 20 WT. OF SECOND PHASE TIN OR BISMUTiH) PATENTEBMIGZII873 ON Q m. a N O- w w v N BEARING MATERIALS This invention relates toan aluminium base alloy for use as a bearing material, for example inthin shell bearings where the alloy requires to be bonded, by rollingfor example, to a steel backing either directly or with an intermediatelayer of metal foil, or after the backing has been plated with, say,nickel or cobalt.

According to the present invention, a bearing alloy comprises aluminiumand more than 1 percent of bismuth by weight. Preferably there is from7-l0 percent bismuth; or for some purposes there may be up to 16 percentby weight bismuth. The aluminium may or not constitute the balance, butwill usually constitute at least 50 percent by weight of the material.

it has been discovered that such a bearing has a surprising ability tosurvive without pick-up or siezure during momentary contact with thejournal when for any reason the oil film thickness becomes locally lessthan the surface roughness. This property is known as compatibility.While softness of the material is a factor in obtaining this property,other factors are relevant, and the property is, in general, littleunderstood. There are three known aluminium-based alloys having a softlow melting point phase which are used for their properties of havinghigh compatibility. These are aluminium/tin, aluminium/lead andaluminium/cadmium.

, Aluminium/bismuth is an alternative and is believed to have surfaceproperties equal to or better than the three alloys for alloys with thesame percentage of the low melting point constituent.

This desirable property of aluminium/bismuth is believed to be due tothe Rhomboidal structure of bismuth. The corrosion resistance of bismuthin engine oils is believed to be betterthan, for example, a similaralloy of aluminium-lead. Tin is conventionally added to aluminium-leadalloys to increase the corrosion resistance to engine oils and in thecomparison we are referring to aluminium-lead without a tin additive.Bismuth is also unusual in that it expands when solidifying, and it isbelieved that this phenomenonmay assist in reducing the tension forcesexisting along the boundary between the soft material and thesurrounding stronger matrix thereby increasing the fatigue strength ofthe material. Clearly the porosity of the alloy is reduced if thebismuth expands to fill the interstices in the surrounding aluminium.

According to a feature of the invention an aluminium base alloy,suitablefor use as a bearing alloy and capable of being bonded to asteel backing contains by weight from 1 percent or3-7 percent bismuthincluding lead impurities, the balance being aluminium except for normalimpurities and from to 3 percent of each of one or more of the elementscopper, nickel and manganese to improve the strength of the aluminiummatrix. in addition up to 5 percent or 1 1 percent silicon may be addedwith, say, 1 percent copper or nickel or both. it may be desirable toinclude a small percentage of a metal or other substance which improvesresistance to corrosion.

The bismuth provides the surface properties required of a bearing alloyand so the defined composition could be only at or near the bearingsurface. However, the whole alloy could also be of uniform composition.

it seems that providing there is bismuth at the bearing surface it isnot necessary to have bismuth throughout the thickness of the bearingmaterial. The bismuth has good surface properties in that it canaccommodate dirt being embodied in it without its bearing propertiesbeing seriously lost and accordingly it is not necessary to provide alead/tin or other plated over-lay on the bearing surface as has beenfound to be necessary in the past for many bearing materials which areprimarily of aluminium. The extra expense of including the hismuth is,therefore, compensated for by avoiding the need for such an overlay.

The invention includes a bearing comprising at least abearing-surface-layer of an alloy as defined, and also a layer of thealloy bonded to a steel or other backing.

It is believed that the fatigue strength of aluminium/- lead alloys isless than that of an aluminium/bismuth alloy having the same proportionof bismuth. The bismuth in an aluminium alloy when rolled down to athickness suitable for bonding to a steel backing tends to form longstringers which readily form into globules when the alloy is annealed.This contrasts with aluminium/lead alloys which do not form globulesreadily on annealing. This property of aluminium/bismuth in conjunctionwith the expansion on solidification, reduces the forces occurring alongthe aluminium boundary as compared with tin or lead and provides apotentially greater fatigue strength. Tests have been carried out onaluminium/bismuth bearing materials which suggest that the percentage ofbismuth in aluminium to provide adequate surface properties can be lessthan those of tin or lead and this also tends to increase the fatiguestrength because less of the softer inclusion is required in thesurrounding matrix of aluminium.

Certain examples of alloys embodying the invention will now bedescribed.

EXAMPLE I A bearing alloy consists of:

Bismuth 3 percent by weight Copper 1 percent by weight Aluminium 96percent by weight The component metals in correct proportions areintroduced into a tun dish and raised to a temperature sufficient tomelt them all, after which a billet of the alloy is cast andsubsequently rolled into a slab with a thickness of about 0.050 inches.The slab is then bonded to a steel backing to make a bearing strip.

EXAMPLE ii A bearing strip is made by the same method described inExample I but the proportions are:

Bismuth 7 percent by weight Nickel 2 percent by weight Silicon 4 percentby weight Aluminium 87 percent by weight EXAMPLE [II A bearing alloywith the following composition:

Bismuth l6 percent by weight Copper l percent by weight Nickel l percentby weight Manganese l percent by weight Silicon ll percent by weightAluminium percent by weight is melted in a tun dish and poured as a slabinto a shallow mould. The alloy is allowed to cool slowly so that mostof the bismuth tends to drop through the aluminium which is muchlighter, so that at the bottom surface the percentage of bismuth ishigh, whereas at the top surface there may be very little bismuth. Thisforms a satisfactory bearing with the high bismuth surface acting as thebearing surface and the low bismuth surface bonded to the steel backing.

EXAMPLE iv A bearing material was made with metals in the followingproportions:

Bismuth l percent by weight Copper 2 percent by weight Silicon 1 percentby weight Aluminium 87 percent by weight The appropriate proportions ofthe metals were mixed in powder form and the composite powder wassintered on a backing and bonded to the backing by rolling.

The accompanying drawing shows some test results obtained with aluminiumbased alloys with bismuth and tin as the second phase. It will be seenthat even an alloy with a tin content of about 18.3 percent by weightits cycle to seizure is not significantly better than an alloy with abismuth content of 13.6 percent. The drawing also shows that an alloycontaining 6.2 percent by weight of bismuth gives 200 cycles of seizurewhile an alloy containing 6.2 percent of tin gives only 140 cycles toseizure.

It is also possible to include bismuth in a shaft which is co-operatingwith a bearing.

There could be 1 percent, 3 percent, 6 percent, 8 percent, 12 percent orl6 percent say, of bismuth by weight, whether the shaft is steel oraluminium or any other metal.

What I claim as my invention and desire to secure by Letters Patent is:

l. A bearing material consisting essentially of bismuth about 16 wt.

silicon about ll wt.

copper about 1 wt.

nickel about 1 wt.

manganese about 1 wt. and

aluminum about 70 wt.

2. A bearing material as claimed in claim 1, in the form of a slab whosethickness is small compared with its length and breadth.

3. A bearing material as claimed in claim 2, in which the proportion ofbismuth at one of the larger surfaces of the slab is greater than theproportion of bismuth at the other of the larger surfaces.

4. A bearing material as claimed in claim 3, in which there is about 16%by weight of bismuth at the one of the larger surfaces.

5. A hearing material as claimed in claim 3, in which there issubstantially no bismuth at the said other of the larger surfaces.

a s s a a

2. A bearing material as claimed in claim 1, in the form of a slab whosethickness is small compared with its length and breadth.
 3. A bearingmaterial as claimed in claim 2, in which the proportion of bismuth atone of the larger surfaces of the slab is greater than the proportion ofbismuth at the other of the larger surfaces.
 4. A bearing material asclaimed in claim 3, in which there is about 16% by weight of bismuth atthe one of the larger surfaces.
 5. A bearing material as claimed inclaim 3, in which there is substantially no bismuth at the said other ofthe larger surfaces.